The present invention is related to the field of Respiratory Syncytial Virus (RSV) vaccines and is particularly concerned with vaccines comprising nucleic acid sequences encoding the fusion (F) protein of RSV.
Respiratory syncytial virus (RSV), a negative-strand RNA virus belonging to the Paramyxoviridae family of viruses, is the major viral pathogen responsible for bronchiolitis and pneumonia in infants and young children (ref. 1xe2x80x94Throughout this application, various references are referred to in parenthesis to more fully describe the state of the art to which this invention pertains. Full bibliographic information for each citation is found at the end of the specification, immediately preceding the claims. The disclosures of these references are hereby incorporated by reference into the present disclosure). Acute respiratory tract infections caused by RSV result in approximately 90,000 hospitalizations and 4,500 deaths per year in the United States (ref. 2). Medical care costs due to RSV infection are greater than $340 M annually in the United States alone (ref. 3). There is currently no licensed vaccine against RSV. The main approaches for developing an RSV vaccine have included inactivated virus, live-attenuated viruses and subunit vaccines.
The F protein of RSV is considered to be one of the most important protective antigens of the virus. There is a significant similarity (89% identity) in the amino acid sequences of the F proteins from RSV subgroups A and B (ref. 3) and anti-F antibodies can cross-neutralize viruses of both subgroups as well as protect immunized animals against infection with viruses from both subgroups (ref. 4). Furthermore, the F protein has been identified as a major target for RSV-specific cytotoxic T-lymphocytes in mice and humans (ref. 3 and ref. 5).
The use of RSV proteins as vaccines may have obstacles. Parenterally administered vaccine candidates have so far proven to be poorly immunogenic with regard to the induction of neutralizing antibodies in seronegative humans or chimpanzees. The serum antibody response induced by these antigens may be further diminished in the presence of passively acquired antibodies, such as the transplacentally acquired maternal antibodies which most young infants possess. A subunit vaccine candidate for RSV consisting of purified fusion glycoprotein from RSV infected cell cultures and purified by immunoaffinity or ion-exchange chromatography has been described (ref. 6). Parenteral immunization of seronegative or seropositive chimpanzees with this preparation was performed and three doses of 50 xcexcg were required in seronegative animals to induce an RSV serum neutralizing titre of approximately 1:50. Upon subsequent challenge of these animals with wild-type RSV, no effect of immunization on virus shedding or clinical disease could be detected in the upper respiratory tract. The effect of immunization with this vaccine on virus shedding in the lower respiratory tract was not investigated, although this is the site where the serum antibody induced by parenteral immunization may be expected to have its greatest effect. Safety and immunogenicity studies have been performed in a small number of seropositive individuals. The vaccine was found to be safe in seropositive children and in three seronegative children (all  greater than 2.4 years of age). The effects of immunization on lower respiratory tract disease could not be determined because of the small number of children immunized. One immunizing dose in seropositive children induced a 4-fold increase in virus neutralizing antibody titres in 40 to 60% of the vaccinees. Thus, insufficient information is available from these small studies to evaluate the efficacy of this vaccine against RSV-induced disease. A further problem facing subunit RSV vaccines is the possibility that inoculation of seronegative subjects with immunogenic preparations might result in disease enhancement (sometimes referred to as immunopotentiation), similar to that seen in formalin inactivated RSV vaccines. In some studies, the immune response to immunization with RSV F protein or a synthetic RSV FG fusion protein resulted in a disease enhancement in rodents resembling that induced by a formalin-inactivated RSV vaccine. The association of immunization with disease enhancement using non-replicating antigens suggests caution in their use as vaccines in seronegative humans.
Live attenuated vaccines against disease caused by RSV may be promising for two main reasons. Firstly, infection by a live vaccine virus induces a balanced immune response comprising mucosal and serum antibodies and cytotoxic T-lymphocytes. Secondly, infection of infants with live attenuated vaccine candidates or naturally acquired wild-type virus is not associated with enhanced disease upon subsequent natural reinfection. It will be challenging to produce live attenuated vaccines that are immunogenic for younger infants who possess maternal virus-neutralizing antibodies and yet are attenuated for seronegative infants greater than or equal to 6 months of age. Attenuated live virus vaccines also have the risks of residual virulence and genetic instability.
Injection of plasmid DNA containing sequences encoding a foreign protein has been shown to result in expression of the foreign protein and the induction of antibody and cytotoxic T-lymphocyte responses to the antigen in a number of studies (see, for example, refs. 7, 8, 9). The use of plasmid DNA inoculation to express viral proteins for the purpose of immunization may offer several advantages over the strategies summarized above. Firstly, DNA encoding a viral antigen can be introduced in the presence of antibody to the virus itself, without loss of potency due to neutralization of virus by the antibodies. Secondly, the antigen expressed in vivo should exhibit a native conformation and, therefore, should induce an antibody response similar to that induced by the antigen present in the wild-type virus infection. In contrast, some processes used in purification of proteins can induce conformational changes which may result in the loss of immunogenicity of protective epitopes and possibly immunopotentiation. Thirdly, the expression of proteins from injected plasmid DNAs can be detected in vivo for a considerably longer period of time than that in virus-infected cells, and this has the theoretical advantage of prolonged cytotoxic T-cell induction and enhanced antibody responses. Fourthly, in vivo expression of antigen may provide protection without the need for an extrinsic adjuvant.
The ability to immunize against disease caused by RSV by administration of a DNA molecule encoding an RSV F protein was unknown before the present invention. In particular, the efficacy of immunization against RSV induced disease using a gene encoding a secreted form of the RSV F protein was unknown. Infection with RSV leads to serious disease. It would be useful and desirable to provide isolated genes encoding RSV F protein and vectors for in vivo administration for use in immunogenic preparations, including vaccines, for protection against disease caused by RSV and for the generation of diagnostic reagents and kits. In particular, it would be desirable to provide vaccines that are immunogenic and protective in humans, including seronegative infants, that do not cause disease enhancement (immunopotentiation).
The present invention relates to a method of immunizing a host against disease caused by respiratory syncytial virus, to nucleic acid molecules used therein, and to diagnostic procedures utilizing the nucleic acid molecules. In particular, the present invention is directed towards the provision of nucleic acid respiratory syncytial virus vaccines.
In accordance with one aspect of the invention, there is provided an immunogenic composition for in vivo administration to a host for the generation in the host of a protective immune response to RSV F protein, comprising a non-replicating vector comprising:
a first nucleotide sequence encoding an RSV F protein or a RSV F protein fragment that generates antibodies and/or cytotoxic T-lymphocytes (CTLs) that specifically react with RSV F protein;
a promoter sequence operatively coupled to the first nucleotide sequence for expression of the RSV F protein, and
a second nucleotide sequence located adjacent the first nucleotide sequence to enhance the immunoprotective ability of the RSV F protein when expressed in vivo from the vector in a host; and
a pharmaceutically-acceptable carrier therefor.
The first nucleotide sequence may be that which encodes a full-length RSV F protein, as seen in FIG. 2 (SEQ ID No: 2). Alternatively, the first nucleotide sequence may be that which encodes an RSV F protein from which the transmembrane region is absent. The latter embodiment may be provided by a nucleotide sequence which encodes a full-length RSV F protein but contains a translational stop codon immediately upstream of the start of the transmembrane coding region, thereby preventing expression of a transmembrane region of the RSV F protein, as seen in FIG. 3 (SEQ. ID No. 4). The lack of expression of the transmembrane region results in a secreted form of the RSV F protein.
The first nucleotide sequence may encode a RSV F protein fragment lacking an autologous RSV F signal peptide sequence and may include, in its place, a sequence encoding a heterologous signal peptide sequence which enhances the level of expression of the RSV F protein. One signal peptide which has been found useful in this regard is the signal peptide of Herpes Simplex Virus I (HSV I)gD. Such enhanced expression levels also lead to improve immunogenicity of the vector at the same dosage level. The first nucleotide sequence may also encode a RSV F protein fragment lacking a transmembrane coding region.
The second nucleotide sequence may comprise a pair of splice sites to prevent aberrant mRNA splicing, whereby substantially all transcribed mRNA encodes the RSV protein. Such second nucleotide sequence may be located between the first nucleotide sequence and the promoter sequence. Such second nucleotide sequence may be that of rabbit xcex2-globin intron II, as shown in FIG. 8 (SEQ ID No: 5).
A vector encoding the F protein and provided by this aspect of the invention may specifically be pXL2 or pXL4 or p82M35B, as seen in FIGS. 5, 7 or 10, respectively.
The promoter sequence may be an immediate early cytomegalovirus (CMV) promoter.
Certain of the vectors provided herein may be used to immunize a host against RSV infection or disease by in vivo expression of RSV F protein lacking a transmembrane region following administration of the vectors. In accordance with a further aspect of the present invention, therefore, there is provided a method of immunizing a host against disease caused by infection with respiratory syncytial virus, which comprises administering to the host an effective amount a of non-replicating vector comprising a first nucleotide sequence encoding an RSV F protein or a RSV F protein fragment that generates antibodies and/or CTLs that specifically react with RSV F protein and a promoter sequence operatively coupled to the first nucleotide sequence for expression of the RSV F protein in the host, which may be a human. The promoter may be an immediate early cytomegalovirus promoter.
The nucleotide sequence may encode a truncated RSV F protein lacking the transmembrane region may be that as described above and/or possess a heterologous signal peptide encoding sequence.
The vector may contain a second nucleotide sequence located adjacent a first nucleotide sequence and effective to enhance the immunoprotective ability of the RSV F protein expressed by the first nucleotide sequence may be used to immunize a host. Specific non-replicating vectors which may be used in this aspect of the invention are those identified as plasmid vectors pXL2, pXL4 and p82M35B in FIGS. 5, 7 and 10 respectively.
The present invention also includes a novel method of using a gene encoding an RSV F protein or a RSV F protein fragment that generates antibodies and/or CTLs that specifically react with RSV F protein to protect a host against disease caused by infection with respiratory syncytial virus, which comprises:
isolating the gene;
operatively linking the gene to at least one control sequence to produce a non-replicating vector, said control sequence directing expression of the RSV F protein when said vector is introduced into a host to produce an immune response to the RSV F protein or fragment thereof, and
introducing the vector into the host.
The procedure provided in accordance with this aspect of the invention may further include the step of:
operatively linking the gene to an immunoprotection enhancing sequence to produce an enhanced immunoprotection by the RSV F protein in the host, preferably by introducing the immunoprotection enhancing sequence between the control sequence and the gene.
In addition, the present invention includes a method of producing a vaccine for protection of a host against disease caused by infection with respiratory syncytial virus, which comprises:
isolating a first nucleotide sequence encoding an RSV F protein or a RSV F protein fragment that generates antibodies and/or CLTs that specifically react with RSV F protein;
operatively linking the first nucleotide sequence to at least one control sequence to produce a non-replicating vector, the control sequence directing expression of the RSV F protein when introduced into a host to produce an immune response to the RSV F protein when expressed in vivo from the vector in a host, and
formulating the vector as a vaccine for in vivo administration.
The first nucleotide sequence further may be operatively linked to a second nucleotide sequence to enhance the immunoprotective ability of the RSV F protein when expressed in vivo from the vector in a host. The vector may be a plasmid vector selected from pXL2, pXL4 and p82M35B. The invention further includes a vaccine for administration to a host, including a human host, produced by this method as well as immunogenic compositions comprising an immunoeffective amount of the vectors described herein.
As noted previously, the vectors provided herein are useful in diagnostic applications. In a further aspect of the invention, therefore, there is provided a method of determining the presence of an RSV F protein in a sample, comprising the steps of:
(a) immunizing a host with a non-replicating vector comprising a first nucleotide sequence encoding an RSV F protein or a RSV F protein fragment that generates antibodies and/or cytotoxic T-lymphocytes (CTLs) that specifically react with RSV F protein and a promoter sequence operatively coupled to the first nucleotide sequence for expression of the RSV F protein in the host to produce antibodies specific for the RSV F protein;
(b) isolating the RSV F protein specific antibodies;
(c) contacting the sample with the isolated antibodies to produce complexes comprising any RSV F protein present in the sample and the RSV F protein-specific antibodies; and
(d) determining production of the complexes.
The non-replicating vector employed to elicit the antibodies may be a plasmid vector which is pXL1, pXL2, pXL3, pXL4 or p82M35B.
The invention also includes a diagnostic kit for detecting the presence of an RSV F protein in a sample, comprising:
(a) a non-replicating vector comprising a first nucleotide sequence encoding an RSV F protein or a RSV F protein fragment that generates antibodies that specifically react with RSV F protein and a promoter sequence operatively coupled to said first nucleotide sequence for expression of said RSV F protein in a host immunized therewith to produce antibodies specific for the RSV F protein;
(b) isolation means to isolate said RSV F protein specific antibodies;
(c) contacting means to contact the isolated RSV F specific antibodies with the sample to produce a complex comprising any RSV F protein present in the sample and RSV F protein specific antibodies; and
(d) identifying means to determine production of the complex.
The present invention is further directed to a method for producing RSV F protein specific polyclonal antibodies comprising the use of the immunization method described herein, and further comprising the step of isolating the RSV F protein specific polyclonal antibodies from the immunized animal.
The present invention is also directed to a method for producing monoclonal antibodies specific for an F protein of RSV, comprising the steps of:
(a) constructing a non-replicating vector comprising a first nucleotide sequence encoding a RSV F protein and a promoter sequence operatively coupled to said first nucleotide sequence for expression of said RSV F protein; and, optionally,
a second nucleotide sequence located adjacent said first nucleotide sequence to enhance the immunoprotective ability of said RSV F protein when expressed in vivo from said vector in a host.
(b) administering the vector to at least one mouse to produce at least one immunized mouse;
(c) removing B-lymphocytes from the at least one immunized mouse;
(d) fusing the B-lymphocytes from the at least one immunized mouse with myeloma cells, thereby producing hybridomas;
(e) cloning the hybridomas;
(f) selecting clones which produce anti-F protein antibody;
(g) culturing the anti-F protein antibody-producing clones; and
(h) isolating anti-F protein monoclonal antibodies.
In this application, the term xe2x80x9cRSV F proteinxe2x80x9d is used to define (1) a full-length RSV F protein, such proteins having variations in their amino acid sequences including those naturally occurring in various strains of RSV, (2) a secreted form of RSV F protein lacking a transmembrane region, and (3) functional analogs of the RSV F protein. In this application, a first protein is a xe2x80x9cfunctional analogxe2x80x9d of a second protein if the first protein is immunologically related to and/or has the same function as the second protein. The functional analog may be, for example, a fragment of the protein or a substitution, addition or deletion mutant thereof. Included are RSV F protein fragments that generate antibodies and/or CTLs that specifically react with RSV F protein.